1 files changed, 72 insertions, 0 deletions
diff --git a/include/linux/scs.h b/include/linux/scs.h
new file mode 100644
index 000000000000..6dec390cf154
--- /dev/null
+++ b/include/linux/scs.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Shadow Call Stack support.
+ *
+ * Copyright (C) 2019 Google LLC
+ */
+
+#ifndef _LINUX_SCS_H
+#define _LINUX_SCS_H
+
+#include <linux/gfp.h>
+#include <linux/poison.h>
+#include <linux/sched.h>
+#include <linux/sizes.h>
+
+#ifdef CONFIG_SHADOW_CALL_STACK
+
+/*
+ * In testing, 1 KiB shadow stack size (i.e. 128 stack frames on a 64-bit
+ * architecture) provided ~40% safety margin on stack usage while keeping
+ * memory allocation overhead reasonable.
+ */
+#define SCS_SIZE		SZ_1K
+#define GFP_SCS			(GFP_KERNEL | __GFP_ZERO)
+
+/* An illegal pointer value to mark the end of the shadow stack. */
+#define SCS_END_MAGIC		(0x5f6UL + POISON_POINTER_DELTA)
+
+/* Allocate a static per-CPU shadow stack */
+#define DEFINE_SCS(name)						\
+	DEFINE_PER_CPU(unsigned long [SCS_SIZE/sizeof(long)], name)	\
+
+#define task_scs(tsk)		(task_thread_info(tsk)->scs_base)
+#define task_scs_sp(tsk)	(task_thread_info(tsk)->scs_sp)
+
+void scs_init(void);
+int scs_prepare(struct task_struct *tsk, int node);
+void scs_release(struct task_struct *tsk);
+
+static inline void scs_task_reset(struct task_struct *tsk)
+{
+	/*
+	 * Reset the shadow stack to the base address in case the task
+	 * is reused.
+	 */
+	task_scs_sp(tsk) = task_scs(tsk);
+}
+
+static inline unsigned long *__scs_magic(void *s)
+{
+	return (unsigned long *)(s + SCS_SIZE) - 1;
+}
+
+static inline bool task_scs_end_corrupted(struct task_struct *tsk)
+{
+	unsigned long *magic = __scs_magic(task_scs(tsk));
+	unsigned long sz = task_scs_sp(tsk) - task_scs(tsk);
+
+	return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC;
+}
+
+#else /* CONFIG_SHADOW_CALL_STACK */
+
+static inline void scs_init(void) {}
+static inline void scs_task_reset(struct task_struct *tsk) {}
+static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; }
+static inline void scs_release(struct task_struct *tsk) {}
+static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
+
+#endif /* CONFIG_SHADOW_CALL_STACK */
+
+#endif /* _LINUX_SCS_H */